Differential local genetic adaptation to pesticide use in organic and conventional agriculture in an aquatic non-target species

Abstract

Pesticide application is an important stressor to non-target species and can profoundly affect ecosystem functioning. Debates continue on the choice of agricultural practices regarding their environmental impact, and organic farming is considered less detrimental compared to conventional practices. Nevertheless, comparative studies on the impacts of both agricultural approaches on the genetic adaptation of non-target species are lacking. We assessed to what extent organic and conventional agriculture elicit local genetic adaptation of populations of a non-target aquatic species, Daphnia magna. We tested for genetic differences in sensitivity of different D. magna populations (n = 7), originating from ponds surrounded by conventional and organic agriculture as well as nature reserves, to pesticides used either in conventional (chlorpyrifos) or organic agriculture (deltamethrin and copper sulfate). The results indicate that D. magna populations differentially adapt to local pesticide use. Populations show increased resistance to chlorpyrifos as the percentage of conventional agriculture in the surrounding landscape increases, whereas populations from organic agriculture sites are more resistant to deltamethrin. While organic agriculture is considered less harmful for non-target species than conventional, both types of agriculture shape the evolution of pesticide resistance in non-target species in a specific manner, reflecting the differences in selection pressure.

Keywords: Daphnia magna; adaptation; deltamethrin; evolution; organic agriculture; resistance.

Figure 1.

Logarithmic concentration (µg l⁻¹) – response (immobilization at 48 h) curves (a,c,e) and average EC₅₀ values (backtransformed) ± CI. (b,d,f), as assessed in a common garden rearing experiment using D. magna, for DTM (a,b), CS (c,d) and CPF (e,f) for each land use type (nature reserve: diamonds, conventional agriculture: triangles, organic agriculture: circles) in which the ponds, from which the D. magna study populations were isolated, were located. Shadowed areas in the left panels corresponds to 95% CI. (a–d) Panels represented in colour correspond to the pesticides allowed in organic agriculture (DTM and CS), and (e,f) panels in grey correspond to pesticide allowed in conventional agriculture (CPF). (Online version in colour.)

Figure 2.

Pesticide resistance expressed as EC₅₀ (median effective concentration) in response to the percentage of agricultural land use type (conventional: (a), organic: (b,c)) within a 200 m radius around the ponds from which study populations of D. magna were collected. Categorical classifications of populations based on land use type are indicated in colour; nature reserves: pink, conventional agriculture: blue and organic agriculture: green. Large circles represent the mean EC₅₀ per clone in each population and small circles represent the EC₅₀ values of each replicate. (a) Panel represented in colour corresponds to the pesticides used in conventional agriculture (CPF), and (b,c) panels in grey correspond to pesticides used in organic agriculture (DTM and CS). (Online version in colour.)